Process of producing artificial proteinaceous fiber utilizing finely divided material in the coagulating bath



Patented Dec. 16, 1947 PROCESS OF PRODUCING ARTIFICIAL PRO- TEINACEOUSFIBER DIVIDED MATERIAL IN THE COAGULAT- ING BATH UTILIZING FINELY LeonLis, West Hartford, and Ralph Horton, Groton, Conn., assignors toAralac, Inc., New York, N. Y., a corporation of Delaware No Drawing.Application June 13, 1945, Serial No. 599,320

3 Claims.

This invention relates to the manufacture of synthetic proteinaceousfibers. More particu- "larly it relates to a process of manufacturingsuch fibers in such a manner as to prevent the adherence of the fibersto each other during their early stages of manufacture in which thesurfaces of the fibers have a soft adherent nature.

Processes have been propsed heretofore, and developed commercially, formaking synthetic fibers from proteinaceous materials, such as theproteins from milk and soybean. In such processes the protein isdispersed in an aqueous medium with an alkaline material, spun into anacidic coagulating bath, and finally hardened with formaldehyde or otherprotein tanning agents.

The process of making these proteinaceous fibers is to be distinguishedfrom the manufacture of rayon in which the chemical or physicalreactions transforming the filaments into a set shape takes placerapidly in a single operation. In the manufacture of viscose rayon, forinstance, the chemical reaction proceeds promptly and setting takesplace rapidly to form the fiber in a finished state in a singleoperation. In making cellulose acetate type of rayon, the fiber iscompletely formed immediately upon the evaporation of the solvent.

In the manufacture of artificial filaments from such protein as zein,the zein is dissolved in alcohol and extruded into a solution offormaldehyde where the reaction proceeds rapidly to form the finishedfiber.

In the manufacture of filaments from an alkali-dispersibleacid-coagulable protein, such as casein, the setting of the filamentstakes place more slowly in a plurality of operations in the preferredtype of process. The protein dispersion, for example, is spun into anacidic coagulating bath, following which the fibers are elongated, andthen passed to a hardening bath. The protein dispersion is veryglue-like in nature and the freshly coagulated filaments as they areremoved from the acidic coagulating bath have a somewhat soft and stickysurface. This characteristic remains more or less until the fibers arehardened.

In the commercial manufacture of filaments from a protein, such ascasein, the output from a large number of spinnerettes is combined intoa tow which may contain from 50,000 to 300,000 filaments. After thesefilaments are withdrawn from the coagulating bath and combined in thetow, they are then passed over suitable stretching apparatus whichelongates the fibers to any desired length. During this elongation thefibers are placed under considerable tension and the force applied forstretching the fibers causes them to press upon each other and thesurfaces of the fibers tend to adhere to each other. When the fibers inthis condition enter the hardening bath, they have a tendency to remainadhering to each other and the individual filaments are not adequatelyand completely hardened. At the conclusion of the hardening operation,the fibers in a tow often remain adherent in which is referred to astight bundles. They do not open up readily into soft fluffy wool-likemasses of fiber which can be processed in the usual fiber fabricatingtechniques.

This difficulty is peculiar particularly to fibers formed fromalkaline-dispersible acid-coagulable proteins which are made in a pluralstage manufacturing process, 1. e., a coagulating stage and a subsequenthardening stage. As has been explained heretofore, this is to becontrasted with rayon manufacture in which a single action, eitherphysical or chemical, takes place to precipitate or set the material infilament form.

In the case of casein fibers, for example, they remain in the somewhatsticky adherent stage from the time they leave the coagulating bathuntil they are hardened. The adherence is aggravated when any attempt ismade to elongate the protein fibers before setting or hardening them.Although adherence is not a problem after hardening, it is desirable, asa practical matter, to accomplish most of the elongation while thefibers are in the coagulated but unhardened state. In this state, whilenon-set,

the fibers are easily elongated. However, they are apt to'adhere to eachother.

We have conceived that materials which would keep the filaments fromsticking together during the coagulating and elongation stage would behighly desirable. Such materials, if of a chemical nature, must notmodify e protein undesirably so that it will deleteriously affect in anyway its physical properties, such as strength, color, etc., and it mustnot affect the chemical properties, and in particular, the dyeingproperties. Physical agents which might separate the fibers but whichadhere and which are attached to the finished fibers would beundesirable. The sticky glue-like nature of the fiber during spinningand elongating is normally thought to have a pronounced adhesive action,and the firm adherence of foreign substances on the surface of thefinished fiber in the large amount that would be 3 necessary foradequate separation is not desirable.

We have discovered, contrary to what might be expected from the knownstate of the prior art and the above considerations, that av proteinfiber. such as a casein fiber, may be formed by spinning a dispersioninto an acidic coagulating bath containing an extremely finely dividedsolid material inert with reference to the coagulating bath to preventadherence of the fibers to each other. This material adheres to thefreshly formed surface of the casein filaments during this stage and.the finely divided material which adheres is sufficient to prevent theadherence of the fibers to each other and eliminates the formation oftight bundles. Furthermore, and this is surprising, during the hardeningof the fiber, at least a part and generally a major portion of thefinely divided material sloughs off or is removed from the surface ofthe fiber. Thus the finished fiber is not modified by the material tosuch an extent as to interfere with its normal use.

In practicing our invention, the proteins to which it may be applied arethe so-called alkalidispersible acid-coagulable proteins. Outstandingexamples are casein from milk, sometimes referred to as animal casein,and the caseins from certain seeds. such as soybean, peanuts,cottonseed, etc., which are often referred to as vegetable casein. Thesecaseins have the characteristic of being dispersible in an alkalinematerial and coagulable in an acid.

The invention will be particularly described with reference to milkcasein as a preferred illustrative embodiment. It is to be understood,however, that other alkali-dispersible acid-coagulableproteinaceous-substances may be used alone or in admixture. The rawmaterial need not be from a single source; for instance, mixtures ofsoybean casein and milk casein may be used, and in addition, naturalprotein fibers, such as wool shoddy may be dispersed and blended with adispersion of milk or soybean casein. The invention also includesdispersions containing a minor proportion of cellulosic dispersions,such as viscose, but in which the problems incident to the manufactureof proteinaceous fibers predominate.

The casein may be dispersed in any of a number of ways known in the artand the particular technique employed is not critical. Any alkalinematerial may be used, preferably caustic soda.

After the dispersion has been appropriately filtered, deaerated andcooled, if necessary, it is pumped through the minute orifices of aspinnerette which is immersed in an acidic coagulating bath.

This bath comprises essentially an acid, such as sulfuric acid inaqueous solution. Other acids may be used, such as acetic, hydrochloric,sulfamic, or the like; sulfuric acid is preferred. The bath may alsocontain advantageously a soluble salt, such as sodium sulfate or sodiumchloride which augments the'action of the acid and possibly has adehydrating action. The acidity of the solution will depend somewhat onthe rate of travel of the fibers through the coagulating liquid and thepH of the protein dispersion. Solutions having an acidity of 1.3 to 2.0pI-I value or higher are preferred. If any tanning agents are included,they should not be in an amount to accomplish any appreciable orsubstantial hardening action.

Included in the coagulating bath, in accordance with the invention, is afinely divided solid material. This must remain as a solid under theacid and other conditions prevailing in the ooagulating bath, andmaterials having this property are referred to as inert. Illustrative ofthese materials are finely ground clay, kaolin, feldspar, diatomaceousearth, talc, soap stone, gypsum, silica, bentonite, asbestos flour,calcium and bariumsulfates, etc., which are referred to as inorganicmaterials. Preferably these should be sufficiently finely divided tostay in suspension in the bath during coagulating, such as a size of theorder of a few microns. Preferably a major portion of the inorganicparticles should be smaller than 5 microns; even colloidal sizeparticles are desirable. The circulation of the coagulating bath, due tothe passage of fibers through it, is generally sufficient to keep thefinely divided material in a state of suspension. Forced circulation,however, may be used. Other materials, such as ground wood flour,leather flour, ground rabbits hair, and other organic inert substancesmay also be used. Because they are lighter they may be larger in size,such as 200 to 300 mesh.

The amount of the finely divided material in the coagulating bath variessomewhat with the one selected, the rate of fiber withdrawal and theextent to which the adherence of the fiber is troublesome. In general,the amount will be within the range of 0.1 to 10% by weight, based uponthe total coagulating bath, preferably 0.2 to

The coagulating bath may contain any of a plurality of auxiliary agentssuggested in the prior art and its composition is not critical, exceptthat it must coagulate the fibers without an appreciable hardeningaction.

After the fiber is so coagulated, it may be elongated and passed to ahardening bath or baths. The hardening bath generally contains analdehyde or a compound yielding one, such as formaldehyde,paraformaldehyde, hexamethylenetetramine, acetaldehyde, paraldehyde,etc. It may also contain a salt, such as sodium sulfate or sodiumchloride which has a dehydrating effeet, and one or more mineral tanningagents, such as alum, etc.

The hardening may be carried out in a plurality of baths, the first bathcontaining a lesser concentration of the hardening agents and the secondbath containing a larger amount. During this treatment, the fiber ishardened sufficiently so that there is no adherence even when passedthrough squeeze rollers. After it is removed from the hardening baths,it may be washed and dried.

After the hardening, the fiber may be acetylated or otherwise treated,in accordance with processes known in the art.

During the hardening action, it has been found that a large portion andgenerally a major portion of the finely divided inert material isremoved from the fiber during the hardening action and possibly also ina subsequent washing operation. Apparently during the hardening action,the surface of the protein fiber shrinks and becomes more firm and theparticles of finely divided solid which have adhered to it, slough off.It appears that these particles adhere to the fiber surface while thefiber is in its coagulated unhardened adhesive stage but that during thehardening, the adhesive character of the surface is eliminated and theability to hold the finely divided solid is greatly reduced. This issurprising, since it might have been expected that the hardening wouldadhere the particles to the surface all the more firmly. This is alsohighly ad vantageous, because fiber containing an appre- 5 ciable amountof the solid would be undesirable for many purposes, clue to themodification of its physical surface characteristics and its chemicalproperties, particularly its dyeing and coloring properties.

As illustrative of this property of removing the finely divided solidfrom the fiber, a dispersion of casein was spun into an acidiccoagulating bath containing 1% of finely divided aluminum silicate.Samples of the fiber after coagulation but before hardening wereanalyzed and were found to contain 0.77% (average) calculated as clay.After the fiber had been hardened in a formaldehyde bath, washed andfinished, in accordance with a commercial method, it was analyzed andfound to contain 0.29%, calculated as clay. This shows that the amountof the clay removed during the hardening action is more than half. Theremoval of the inert material during the hardening was also evidenced bythe fact that large quantities accumulated in the hardening tanks.

The fiber produced in accordance with the invention may be put to anyuse for which synthetic proteinaceous fiber is now employed. It has gooddyeing properties and the small amount of the finely divided solid whichadheres to it does not interfere with any of its normal uses.

It will be obvious that the invention contemplates many variations inthe exact procedure that can be employed, in the composition of thedispersion and various treating baths, and in the finely divided solidmaterial, and the invention is intended to cover all of the same as areincluded within the following claims,

We claim;

1. In a process of manufacturing synthetic proteinaceous fibercomprising an alkali-dispersible acid-coagulable protein, in whichprocess the fibers are elongated after spinning and before hardening andduring which there is a marked tendency for the fibers to adhere to eachother, the steps comprising spinning a dispersion of said protein intoan acidic coagulating bath in which is suspended particles of a finelydivided solid material inert with respect to the coagulating bath andsaid protein to form filaments in a coagulated but unhardened state andupon the freshly coagulated surface of which filaments said particlesadhere, elongating a plurality of said filaments by stretching thefilaments while they are in said unhardened condition during which theparticles on the filament surface inhibit the adherence of the fibers toeach other, passing the elongated filaments into a protein hardeningbath comprising formaldehyde, holding the fi1aments in the hardeningbath so as to harden the protein and cause the filaments to lose theadhesive character of their surface, whereby a major portion of saidparticles slough off from the surface of the filaments during the normalhardening and subsequent washing steps and the fiber is not modified bythe treatment with the particles to such an extent as to interfere withits normal use.

2. The process of claim 1 in which the particles of finely divided solidare particles of finely divided clay.

3. The process of claim 1 in which the alkalidispersible acid-coagulatedprotein comprises milk casein.

LEON LIS. RALPH HORTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,211,961 Meigs Aug. 20, 19402,290,789 Wormell July 21, 1942 2,297,397 Ferretti Sept. 29, 19422,348,761 Sturken May 16, 1944 2,361,713 Sturken Oct. 31, 1944

